text: There are few examples of seven-carbon sugars in nature, among which are:
  * sedoheptulose or -altro-heptulose (a ketose), an intermediate in the Calvin cycle and in lipid A biosynthesis
  * mannoheptulose (a ketose), found in avocadoes
  * -glycero--manno-heptose (an aldose), a late intermediate in lipid A biosynthesis.